Chemically modified asphalts, which are produced by reacting asphalt, a vinyl aromatic monomer and a rubbery polymer, are known in the art and are exemplified by U.S. Pat. No. 4,273,685 (hereby incorporated by reference). Such a chemically modified asphalt has been employed for purposes of the repair and maintenance of roads, highways, parking lots, driveways, airport runways and the like (hereinafter highway repair and maintenance) as well as for purposes of waterproofing bridge decks. It has also been used to coat fibrous glass reinforcements.
In the above incorporated patent applications, laminates are disclosed which are suitable for highway repair and maintenances purposes which include a membrane comprised of an asphaltic coated fibrous glass reinforcement material having a pressure sensitive adhesive layer on one side of the laminate. The pressure sensitive adhesive is adapted for bonding to cementitious substrates, such as Portland cement substrates, and asphaltic concrete substrates. The asphaltic coating on the fibrous glass reinforcement is a chemically modified asphalt which is also the reaction product of asphalt, a polymerizable vinyl aromatic monomer and a rubber polymer. A chemically modified asphalts of the above type, which has received extensive evaluation, is the reaction product of an AC-20 paving grade asphalt, styrene, and an elastomeric styrene-butadiene copolymer. AC-20 paving grade asphalt has a viscosity of about 500-550 cps. at 260.degree. F. and about 100-120 cps. at 300.degree. F. and a penetration of about 40 to about 60 or 65, and the styrene-butadiene copolymer which has been employed is commercially available, and indicated in the literature, to be an A-B type, linear block elastomer. Such chemically modified asphalts as represented by the use of the above-indicated ingredients for their formation, have many outstanding properties, but they are deficient in certain respects. Such compositions could receive more widespread adoption if their elastic recovery rate could be increased, if their viscosity stability could be increased as well as reducing their viscosity, and if they were less tacky and if they would impregnate glass fiber bundles. By providing such improvements in the properties, the materials would show improved operational characteristics when employed for highway repair and maintenance purposes, as well as for waterproofing coatings on bridgedeck membranes. Additionally, they would more easily be suitable for use as hot melt adhesives or solvent base adhesives and for various spray coating applications. Thus, by providing for a decreased viscosity, the materials would be easier to spray and could be used directly in the field, or in forming the above indicated type laminates, at lower temperatures. Additionally, by increasing their viscosity stability, more reliable results will be obtained both in the field and in forming such laminates, and the improved elastic recovery will provide improved results in actual field uses. Finally, by providing for a less tacky material, the laminates of the type generally discussed above can more easily be handled because of minimal tendency for interlaminate adhesion. Moreover, less tack will result in less tire tracking which is quite significant in highway repair and maintenance. Finally, by providing for material which is capable of impregnating glass fiber bundles, the abrasion resistance between the individual filaments of the bundle is greatly decreased and, consequently, the tensile strength of such impregnated glass fiber bundles is increased, thereby providing for improved field operation.
For further reference to membranes which include a supporting material and an asphaltic coating which is not a pressure sensitive adhesive on one side and, on the opposite side, an asphaltic coating which is a pressure sensitive adhesive, reference may be had to U.S. Pat. Nos. 3,741,856 and 3,900,102 which claim or disclose such laminated structures.
Thus, in accordance with the present invention, improvements are provided in chemically modified asphalts of the type which are the reaction product of asphalt, a vinyl aromatic monomer and a rubbery polymer, wherein the improved composition has an increased elastic recovery rate, increased viscosity stability, is less tacky and has lower viscosity, and can impregnate fiber glass bundles which are comprised of a multitude of individual glass fiber filaments. Such improved compositions are obtained by employing as the rubbery polymer a thermoplastic rubber, generally linear, non radial, block copolymer of styrene and butadiene having polystyrene end blocks and a polybutadiene mid block. Thus, in contrast to the above indicated A-B elastomers, the presently employed thermoplastic rubbers may generally be viewed as being of the A-B-A type, linear block copolymers.